In a data communication network, a network element device will be frequently restarted due to various reasons such as software reinstallation or upgrade, software failure or primary-standby switching of a processor running control software. Restart of the network element device may be divided into two classes: a first class of restart, which may cause failure of a forwarding function of the network element device along with the restart of the control software, will inevitably trigger re-convergence of a forwarding route in a network and will affect a service traffic in the network accordingly; and a second class of restart, which can ensure that the forwarding function of the network element device keeps normally running in a restart process of the control software, will not inevitably trigger re-convergence of the forwarding route in the network and will not affect the service traffic in the network accordingly.
In view of the second class of restart, in order to avoid re-convergence of the forwarding route in the network, it is necessary to make some extensions on basic routing protocols such as an Open Shortest Path First (OSPF) protocol, an Intermediate System to Intermediate System (IS-IS) protocol and a Border Gateway Protocol (BGP), and to add corresponding protocol messages and protocol flows. A non-stop forwarding restart process implemented by the network element device supporting these protocol extensions is called as GR. The international standard organization Internet Engineering Task Force (IETF) released RFC 3623 in November, 2003 and RFC 5187 in June, 2008 respectively, and specified how to extend the OSPF protocol so as to support GR of a network element device running the OSPF protocol. The IETF released RFC 5306 in October, 2008, and specified how to extend the IS-IS protocol so as to support GR of a network element device running the IS-IS protocol. The IETF released RFC 4724 in January, 2007, and specified how to extend the BGP so as to support GR of a network element device running the BGP.
With the proposal of a concept of Software Defined Network (SDN) and the development of an application of the SDN, an OpenFlow technology serving as an SDN core technology is in a rapid development stage, and an OpenFlow network constructed using the OpenFlow technology currently has been more and more applied to actual production and living. An OpenFlow network adopts an architecture where a control plane and a forwarding plane (also called as a data plane or a user plane) are separated. FIG. 1 is an architecture diagram of an OpenFlow network component according to the related art. As shown in FIG. 1, the control plane of the OpenFlow network is implemented by an OpenFlow controller, the OpenFlow controller is a device having a powerful computing capability, and a specific form of the device may be a personal computer, a server or a server cluster. The forwarding plane of the OpenFlow network is implemented by an OpenFlow switch, the OpenFlow switch is a device having a powerful switching capability, and a specific form of the device is a network element device equipped with a plurality of network ports to process and forward a message based on a flow table. A network application program is App software similar to an App running on a terminal device such as a mobile phone and a tablet computer, and is configured to complete deployment and/or modification of a certain network service. An interface between the OpenFlow controller and the OpenFlow switch runs an OpenFlow protocol, and the network application program may call the OpenFlow controller via a Northbound Interface (NBI) so as to achieve operations on the OpenFlow network. The international standard organization Open Networking Foundation (ONF) is in charge of specifying and modifying the OpenFlow protocol and the NBI, and an OpenFlow switch specification 1.4.0 version formally released by the ONF in October, 2013 specifies an OpenFlow protocol flow and a message processing flow inside the OpenFlow switch. An OpenFlow switch specification specifies that when connection between the OpenFlow switch and the OpenFlow controller is interrupted, the OpenFlow switch will enter a fail secure mode or a fail standalone mode: the OpenFlow switch entering the fail secure mode still forwards a received service message according to the flow table and will directly discard the service message requiring to be sent to the OpenFlow controller; and the OpenFlow switch entering the fail standalone mode will forward the service message by adopting a non-flow table forwarding manner, namely utilizing a traditional forwarding table, and the fail standalone mode is merely applied to a hybrid network element device supporting both flow table forwarding and traditional forwarding table forwarding simultaneously. The above OpenFlow switch specification merely specifies a behaviour of the OpenFlow switch after the connection between the OpenFlow switch and the OpenFlow controller is interrupted, and due to lack of consideration of how to support GR of the OpenFlow switch, behaviour specifications of the OpenFlow switch and the OpenFlow controller before and after the GR of the OpenFlow switch are not provided. Consequently, once the OpenFlow switch is restarted and the interruption of the connection between the OpenFlow switch and the OpenFlow controller will to be triggered, the OpenFlow controller will delete the OpenFlow switch and all network connection of the OpenFlow switch from a self-stored network topology, thereby re-computing routes and update flow tables of all affected OpenFlow switches in the network. After the restart of the OpenFlow switch is completed and re-establishes an OpenFlow protocol connection with the OpenFlow controller, the OpenFlow controller will re-discover all network connections of the OpenFlow switch and add the network element device into the self-stored network topology, thereby re-computing routes and update flow tables of all affected OpenFlow switches in the network.
As a result, the problem that GR of an OpenFlow switch cannot be achieved exists in the related art.